Alternative pathway of fetal androgen synthesis (WP4524)

Homo sapiens

The development of sexual organs in humans is still not completely understood at the molecular level, controlled through the chromosomal difference between men and women. Steroids related to sexual development can have a temporary or permanent effects. Androgens are the leading compounds differentiating between (among other sexual organs) the internal and external genitalia of men. Next to the classical pathway of androgen synthesis (see []), alternative pathways are known, which make use of either selective expression patterns of isoenzymes or alternate enzymes. As an alternative, a socalled 'backdoor pathway', which can create dihydrotestosterone (DHT), skipping testosterone. Several enzymes between the classical and backdoor pathway are shared, however the later one utilises one unique enzyme, 3-alpha hydroxysteroid dehydrogenase 3 (gene: AKR1C2). Even though the relevance of this backdoor pathway for humans is not completely clear yet, mutations in the human AKR1C2 gene can lead to disordered sexual differentiation. This finding would indicate that both the classical and the alternative pathway are needed for normal development of male genitalia in humans. For more information on androgens, see Hiort (2013 []), and for more information on the disease linked to this pathway, please visit Chapter 37 of the book of Blau (ISBN 3642403360 (978-3642403361)).
last edited


Eline Sanders , Denise Slenter , Egon Willighagen , Irene Hemel , Friederike Ehrhart , Eric Weitz , and Finterly Hu

Cited In

Are you planning to include this pathway in your next publication? See How to Cite and add a link here to your paper once it's online.


Homo sapiens


Inborn Errors of Metabolism (IEM) Pathways Rare Diseases


Pathway Ontology: testosterone biosynthetic pathway altered steroid biosynthetic pathway steroid hormone metabolic pathway steroid metabolic pathway altered isoprenoid biosynthetic pathway cholesterol metabolic pathway steroid hormone biosynthetic pathway disease pathway

Disease Ontology: steroid inherited metabolic disorder


Label Type Compact Identifier Comment
Dihydrotestosterone (DHT) Metabolite chebi:16330
Pregnenolone Metabolite chebi:16581
Androsterone Metabolite chebi:16032
17-Hydroxyallopregnanolone Metabolite chebi:11909
DHEA Metabolite chebi:28689
17-Hydroxypregnenolone Metabolite wikidata:Q2064889
17-Hydroxyprogesterone Metabolite hmdb:HMDB0000374
NADP+ Metabolite chebi:58349
17-hydroxydihydroprogesterone Metabolite chebi:36723
NADPH Metabolite chebi:57783
Androstanedione Metabolite chebi:15994
Androstenedione Metabolite chebi:16422
androst-4-ene-3,17-dione Metabolite chebi:16422
Progesterone Metabolite chebi:17026
Cholesterol Metabolite chebi:16113
NAD+ Metabolite chebi:57540
Testosterone Metabolite chebi:17347
Androstanediol Metabolite chebi:27727
NADH Metabolite chebi:57945
NADP+ Metabolite chebi:58349
NADPH Metabolite chebi:57783
NAD+ Metabolite chebi:57540
NADH Metabolite chebi:57945
P450scc GeneProduct ensembl:ENSG00000140459
STAR GeneProduct ensembl:ENSG00000147465
5-alpha-reductase 1 GeneProduct ensembl:ENSG00000277893
17-beta-HSD GeneProduct ensembl:ENSG00000130948
3-beta-HSD GeneProduct ensembl:ENSG00000203859
AKR1C2/4 GeneProduct ensembl:ENSG00000151632
AKR1C4 GeneProduct ensembl:ENSG00000198610
P450c17 GeneProduct ensembl:ENSG00000148795
3-beta-HSD GeneProduct ensembl:ENSG00000203859
17-beta-HSD3 GeneProduct ensembl:ENSG00000130948
Cytb5 Protein uniprot:P00167
3 HSD Protein uniprot:P26439 Aka HSD3B2; 3 beta-hydroxysteroid dehydrogenase type II
AKR1C2 Protein uniprot:P52895 Responsible protein found through Rhea (not part of Blau book)
P450c17 Protein ensembl:ENSG00000148795
RODH Protein uniprot:O14756
POR Protein uniprot:P16435 Function:'This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes' []
POR Protein uniprot:P16435
5-alpha-reductase 2 Protein uniprot:P31213
P450c17 Protein ensembl:ENSG00000148795
P450c17 Protein ensembl:ENSG00000148795
P450c17 Protein uniprot:P05093 Function:'Conversion of pregnenolone and progesterone to their 17-alpha-hydroxylated products and subsequently to dehydroepiandrosterone (DHEA) and androstenedione. Catalyzes both the 17-alpha-hydroxylation and the 17,20-lyase reaction. Involved in sexual development during fetal life and at puberty' []
P450c17 Protein ensembl:ENSG00000148795
P450c17 Protein ensembl:ENSG00000148795
POR Protein uniprot:P16435 Function:'This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes' []
P450c17 Protein ensembl:ENSG00000148795
P450c17 Protein ensembl:ENSG00000148795
POR Protein uniprot:P16435 Function:'This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes' []
P450c17 Protein ensembl:ENSG00000148795
P450c17 Protein ensembl:ENSG00000148795
POR Protein uniprot:P16435 Function:'This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes' []
POR Protein uniprot:P16435 Function:'This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes' []
AKR1C2 Protein uniprot:P52895 Responsible protein found through Rhea (not part of Blau book)


  1. Blau N, Duran M, Gibson KM, Dionisi-Vici C. Physician’s Guide to the Diagnosis, Treatment, and Follow-Up of Inherited Metabolic Diseases [Internet]. Springer; 2014. 867 p. Available from: OpenLibrary Worldcat
  2. Goldstein JL, Wilson JD. Genetic and hormonal control of male sexual differentiation. J Cell Physiol. 1975 Apr;85(2 Pt 2 Suppl 1):365–77. PubMed Europe PMC Scholia
  3. Moore RJ, Griffin JE, Wilson JD. Diminished 5alpha-reductase activity in extracts of fibroblasts cultured from patients with familial incomplete male pseudohermaphroditism, type 2. J Biol Chem. 1975 Sep 25;250(18):7168–72. PubMed Europe PMC Scholia
  4. Wilson JD. Dihydrotestosterone formation in cultured human fibroblasts. Comparison of cells from normal subjects and patients with familial incomplete male pseudohermaphroditism, Type 2. J Biol Chem. 1975 May 10;250(9):3498–504. PubMed Europe PMC Scholia
  5. Burstein S, Middleditch BS, Gut M. Mass spectrometric study of the enzymatic conversion of cholesterol to (22R)-22-hydroxycholesterol, (20R,22R)-20,22-dihydroxycholesterol, and pregnenolone, and of (22R)-22-hydroxycholesterol to the lgycol and pregnenolone in bovine adrenocortical preparations. Mode of oxygen incorporation. J Biol Chem. 1975 Dec 10;250(23):9028–37. PubMed Europe PMC Scholia
  6. Andersson S, Russell DW. Structural and biochemical properties of cloned and expressed human and rat steroid 5 alpha-reductases. Proc Natl Acad Sci U S A. 1990 May;87(10):3640–4. PubMed Europe PMC Scholia
  7. Hanukoglu I, Spitsberg V, Bumpus JA, Dus KM, Jefcoate CR. Adrenal mitochondrial cytochrome P-450scc. Cholesterol and adrenodoxin interactions at equilibrium and during turnover. J Biol Chem. 1981 May 10;256(9):4321–8. PubMed Europe PMC Scholia
  8. Geissler WM, Davis DL, Wu L, Bradshaw KD, Patel S, Mendonca BB, et al. Male pseudohermaphroditism caused by mutations of testicular 17 beta-hydroxysteroid dehydrogenase 3. Nat Genet. 1994 May;7(1):34–9. PubMed Europe PMC Scholia
  9. Auchus RJ, Lee TC, Miller WL. Cytochrome b5 augments the 17,20-lyase activity of human P450c17 without direct electron transfer. J Biol Chem. 1998 Feb 6;273(6):3158–65. PubMed Europe PMC Scholia
  10. Makridakis NM, di Salle E, Reichardt JK. Biochemical and pharmacogenetic dissection of human steroid 5 alpha-reductase type II. Pharmacogenetics. 2000 Jul;10(5):407–13. PubMed Europe PMC Scholia
  11. Penning TM, Burczynski ME, Jez JM, Hung CF, Lin HK, Ma H, et al. Human 3alpha-hydroxysteroid dehydrogenase isoforms (AKR1C1-AKR1C4) of the aldo-keto reductase superfamily: functional plasticity and tissue distribution reveals roles in the inactivation and formation of male and female sex hormones. Biochem J. 2000 Oct 1;351(Pt 1):67–77. PubMed Europe PMC Scholia
  12. Chetyrkin SV, Belyaeva OV, Gough WH, Kedishvili NY. Characterization of a novel type of human microsomal 3alpha -hydroxysteroid dehydrogenase: unique tissue distribution and catalytic properties. J Biol Chem. 2001 Jun 22;276(25):22278–86. PubMed Europe PMC Scholia
  13. Munro AW, Noble MA, Robledo L, Daff SN, Chapman SK. Determination of the redox properties of human NADPH-cytochrome P450 reductase. Biochemistry. 2001 Feb 20;40(7):1956–63. PubMed Europe PMC Scholia
  14. Chetyrkin SV, Hu J, Gough WH, Dumaual N, Kedishvili NY. Further characterization of human microsomal 3alpha-hydroxysteroid dehydrogenase. Arch Biochem Biophys. 2001 Feb 1;386(1):1–10. PubMed Europe PMC Scholia
  15. Shafqat N, Marschall H-U, Filling C, Nordling E, Wu X-Q, Björk L, et al. Expanded substrate screenings of human and Drosophila type 10 17beta-hydroxysteroid dehydrogenases (HSDs) reveal multiple specificities in bile acid and steroid hormone metabolism: characterization of multifunctional 3alpha/7alpha/7beta/17beta/20beta/21-HSD. Biochem J. 2003 Nov 15;376(Pt 1):49–60. PubMed Europe PMC Scholia
  16. Mast N, Norcross R, Andersson U, Shou M, Nakayama K, Bjorkhem I, et al. Broad substrate specificity of human cytochrome P450 46A1 which initiates cholesterol degradation in the brain. Biochemistry. 2003 Dec 9;42(48):14284–92. PubMed Europe PMC Scholia
  17. Mindnich R, Haller F, Halbach F, Moeller G, Hrabé de Angelis M, Adamski J. Androgen metabolism via 17beta-hydroxysteroid dehydrogenase type 3 in mammalian and non-mammalian vertebrates: comparison of the human and the zebrafish enzyme. J Mol Endocrinol. 2005 Oct;35(2):305–16. PubMed Europe PMC Scholia
  18. Kolar NW, Swart AC, Mason JI, Swart P. Functional expression and characterisation of human cytochrome P45017alpha in Pichia pastoris. J Biotechnol. 2007 May 10;129(4):635–44. PubMed Europe PMC Scholia
  19. Pechurskaya TA, Lukashevich OP, Gilep AA, Usanov SA. Engineering, expression, and purification of “soluble” human cytochrome P45017alpha and its functional characterization. Biochemistry (Mosc). 2008 Jul;73(7):806–11. PubMed Europe PMC Scholia
  20. Guengerich FP, Martin MV, Sohl CD, Cheng Q. Measurement of cytochrome P450 and NADPH-cytochrome P450 reductase. Nat Protoc. 2009;4(9):1245–51. PubMed Europe PMC Scholia
  21. Mast N, Annalora AJ, Lodowski DT, Palczewski K, Stout CD, Pikuleva IA. Structural basis for three-step sequential catalysis by the cholesterol side chain cleavage enzyme CYP11A1. J Biol Chem. 2011 Feb 18;286(7):5607–13. PubMed Europe PMC Scholia
  22. Sandee D, Miller WL. High-yield expression of a catalytically active membrane-bound protein: human P450 oxidoreductase. Endocrinology. 2011 Jul;152(7):2904–8. PubMed Europe PMC Scholia
  23. Strushkevich N, MacKenzie F, Cherkesova T, Grabovec I, Usanov S, Park H-W. Structural basis for pregnenolone biosynthesis by the mitochondrial monooxygenase system. Proc Natl Acad Sci U S A. 2011 Jun 21;108(25):10139–43. PubMed Europe PMC Scholia
  24. Flück CE, Meyer-Böni M, Pandey AV, Kempná P, Miller WL, Schoenle EJ, et al. Why boys will be boys: two pathways of fetal testicular androgen biosynthesis are needed for male sexual differentiation. Am J Hum Genet. 2011 Aug 12;89(2):201–18. PubMed Europe PMC Scholia
  25. Hiort O. The differential role of androgens in early human sex development. BMC Med. 2013 Jun 24;11:152. PubMed Europe PMC Scholia
  26. Weber S, Salabei JK, Möller G, Kremmer E, Bhatnagar A, Adamski J, et al. Aldo-keto Reductase 1B15 (AKR1B15): a mitochondrial human aldo-keto reductase with activity toward steroids and 3-keto-acyl-CoA conjugates. J Biol Chem. 2015 Mar 6;290(10):6531–45. PubMed Europe PMC Scholia
  27. Engeli RT, Rhouma BB, Sager CP, Tsachaki M, Birk J, Fakhfakh F, et al. Biochemical analyses and molecular modeling explain the functional loss of 17β-hydroxysteroid dehydrogenase 3 mutant G133R in three Tunisian patients with 46, XY Disorders of Sex Development. J Steroid Biochem Mol Biol. 2016 Jan;155(Pt A):147–54. PubMed Europe PMC Scholia
  28. Simonov AN, Holien JK, Yeung JCI, Nguyen AD, Corbin CJ, Zheng J, et al. Mechanistic Scrutiny Identifies a Kinetic Role for Cytochrome b5 Regulation of Human Cytochrome P450c17 (CYP17A1, P450 17A1). PLoS One. 2015 Nov 20;10(11):e0141252. PubMed Europe PMC Scholia
  29. Mak PJ, Gregory MC, Denisov IG, Sligar SG, Kincaid JR. Unveiling the crucial intermediates in androgen production. Proc Natl Acad Sci U S A. 2015 Dec 29;112(52):15856–61. PubMed Europe PMC Scholia
  30. Fouad Mansour M, Pelletier M, Tchernof A. Characterization of 5α-reductase activity and isoenzymes in human abdominal adipose tissues. J Steroid Biochem Mol Biol. 2016 Jul;161:45–53. PubMed Europe PMC Scholia
  31. Bhatt MR, Khatri Y, Rodgers RJ, Martin LL. Role of cytochrome b5 in the modulation of the enzymatic activities of cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1). J Steroid Biochem Mol Biol. 2017 Jun;170:2–18. PubMed Europe PMC Scholia
  32. Yoshimoto FK, Gonzalez E, Auchus RJ, Guengerich FP. Mechanism of 17α,20-Lyase and New Hydroxylation Reactions of Human Cytochrome P450 17A1: 18O LABELING AND OXYGEN SURROGATE EVIDENCE FOR A ROLE OF A PERFERRYL OXYGEN. J Biol Chem. 2016 Aug 12;291(33):17143–64. PubMed Europe PMC Scholia